This invention relates in general to data collection systems and, more particularly, in one embodiment to an improved apparatus and method for monitoring conditions at a predetermined location.
During the course of the last decade, automatic meter reading (AMR) systems have evolved from a largely theoretical concept to a proven technology. The primary application for AMR systems is to collect utility meter readings from customer premises via the existing public telephone network.
Most utility meter readings are now collected manually by each utility on a regular basis. At great expense, a water meter reader drives or walks to each home or business. Yet another meter reader drives mr walks to each home or business to read the electric meters. Still additional meter readers read gas meters and other utilities. This manual utility consumption data collection effort represents a very substantial expense to the utilities involved. The economic benefit and labor saving potential for AMR systems, which automate this otherwise manual data collection task, become readily apparent.
In addition, a properly designed AMR system is also capable of collecting meter readings from a plurality of utility meters located on customer premises. Since most American households purchase metered commodities from several different utility companies (electricity, water, gas, etc.), the readings from all utility meters at a single residence can be simultaneously collected thereby increasing the efficiency of the data collection process even further. Automatically collecting these readings via existing customer telephone lines is clearly an advantageous method and one certainly less error prone than the manual ("meterman") method which it replaces.
In addition to the obvious economic benefits, AMR systems also provide features which cannot be obtained practically by manual data collection methods. For instance, meters at customer premises can be read at will thereby providing time of day readings and peak or excessive or random interval measurements to be made at very little cost. Under such circumstances, the payback period to recover the initial installation costs is very short. The economic and technical feasibility of AMR systems, coupled with the flexible performance and monitoring capabilities which they inherently provide, make it very likely that these systems will ultimately replace the inefficient manual methods now being used to collect utility meter readings from businesses, residences and industry.
The following is a brief discussion of the operation of one conventional AMR system which demonstrates the basic structure and the elements of such a system. FIG. 1 shows a simplified block diagram of several residences 10, factories 15 and businesses 20 coupled via trunk lines 25 to a central office (CO) 30. At first glance, the operation of AMR systems may seem deceptively straightforward. However, the pragmatic aspects of designing the individual components within the system has been a major obstacle hindering the implementation of AMR systems. Many of the problems encountered in the design of AMR systems involve the vagaries of the telephone system itself and the wide variations in certain relevant parameters thereof. All these factors, coupled with a requirement for any AMR equipment placed at customer premises to be highly reliable while simultaneously being cost effective, combine to make the design of this equipment far from an elementary task. It is only very recently that equipment capable of meeting the stringent requirements of this technology has become available.
As seen in FIG. 1, a typical AMR system uses the same telephone lines which provide normal subscriber telephone voice service without any alteration of telephone company equipment. When an AMR system is present on a subscriber's telephone line, there is no perceivable difference to the customer as to how the voice telephone system operates in comparison to an identical telephone system without AMR capability. In AMR systems, it is very desirable to have a minimal impact on the design of the existing telephone network.
FIG. 2 is a block diagram of the additional equipment required at the customer's premises (shown as 10, 15 or 20 in FIG. 1) to make the operation of the AMR system possible. To provide non-intrusive operation with respect to the voice operation of the subscriber phone line, the AMR equipment at the customer's premises simply "bridges" or parallels the existing telephone circuits. If properly designed, the AMR equipment will not negatively affect the operation of that telephone equipment.
As seen in FIG. 2, an MIU (meter interface unit) 35 is connected in parallel with the subscriber telephone line 25 at each remote site or customer premises. Connected in a similar parallel manner to the phone line are the telephone set 40 and other communications devices 45 which the customer might use such as answering machines, FAX telecopiers, computer modems and the like. For purposes of this discussion, one user device will not be distinguished from another and, in this context, a "telephone set" is used to mean any one of the user supplied devices.
It is again emphasized that the MIU connects to or bridges the phone line without adversely effecting the operation of the other devices on the line and that this property is not an inherent feature of the telephone network. Had the concept of a voice telephone system developed simultaneously with that of an AMR system, the need for the very specialized technology required to couple an MIU to a subscriber phone line may not have been encountered. However, such was not the case in that voice telephone systems clearly developed prior to AMR systems. For this reason, significant problems are encountered when attempting to get AMR systems and voice messaging systems to coexist on the same telephone line without one interfering with the other.
While these user supplied devices (phone, fax, modem, etc.) are under the direct control of the consumer who provides them, the MIU is part of a separate network belonging to a utility company or utility meter agency which needs to collect utility use data. Since the MIU and the telephone set cannot function simultaneously on the same subscriber line, one or the other must have priority. Since the AMR system is automated and the telephone company will not tolerate any degradation in subscriber telephone service, the choice, by default, is that the telephone subscriber or user must have priority over any AMR function.
Attached to MIU 35 are one or more electronic registers 50 which are physically attached to the bodies of utility meters 55. These registers can be read electronically by the MIU but may also have the same dials as their mechanical counterparts. These registers 50 serve to electronically collect the amount of metered commodity delivered to a customer, just as mechanical registers record such information mechanically with indicating dials. In most AMR systems, the electronic register converts the mechanical motion of a flow sensor into a serial format, similar to the familiar RS-232 format, which can be electronically transferred when the device is interrogated in a prescribed manner. Such an arrangement minimizes the number of wires required to electrically interface the MIU to the electronic register.
Each of the above mentioned components of an AMR system is strategically and logically placed in accordance with its function. The MIU is placed near a telephone line and is connected to one of more utility meters which are each placed by the corresponding utility in an appropriate location. For example, an MIU might be placed where the phone line enters the customer premises while the water meter is located in an underground pit, the electric meter at the power drop, and the gas meter in still a different location. It is, of course, possible to combine the MIU and electronic register functions although not very practical unless the utility installation has been specially configured, which most existing sites have not. Furthermore, since each of the utility meters is owned by a different utility company which is responsible for calibrating and guaranteeing their accuracy, the MIU and electrically encoding register functions are most likely to remain as functionally separate devices. The MIU serves as the hardware interface between the utility meters (equipped with electronic registers) and the telephone line. As such, it is desirable, although not required, that the MIU be powered directly from the phone line without any reliance on external, power sources or batteries which would increase maintenance costs.
As the primary interface between the phone line and utility meter apparatus, the MIU also serves another extremely important purpose, namely that of electrically isolating the telephone line from the surrounding electrical environment. This isolation barrier is necessary to prevent electrical transients from damaging the MIU or utility apparatus attached to the MIU and vice-a-versa. In addition, since this isolation barrier provides protection to service personnel and customers alike, the phone company will generally not permit the installation of equipment which does not provide a specified degree of protection.
As seen in the block diagram of central office 30 in FIG. 3, a single central office site serves a plurality of remote users. Central office 30 includes a central office "switch" 60 and one or more "punch down blocks" 65. Phone lines 25 are essentially a bundle of wires which enter central office 30 and which are connected to one or more of punch down blocks 65. From punch down blocks 65, the subscriber lines pairs within this wire bundle are connected to central office switch 60. Each subscriber line has a known port on the central office switch 60 which can be uniquely addressed by calling a specific telephone number.
Associated with the central office switch 60 is a test trunk 67 which the telephone company uses to test subscriber lines attached to the switch 60. These tests help the service provider to ascertain the condition of any or all of the cable pairs attached to the switch, for maintenance purposes. Although most subscribers are unaware of such a function, the telephone company routinely checks the condition of the telephone line on a regular basis. Since these testing capabilities are an integral part of the central office switch design, the test trunk provides an ideal interface point for an AMR controller 70. By using the test trunk, AMR controller 70 utilizes capabilities already incorporated into the switch by design, to minimize disruptions to subscriber service caused by activity on the test trunk. Thus test trunk 67 is the access point for AMR controller 70 to selectively connect to a given MIU. Part of the AMR controller function is to maintain a table of "phone" numbers which can be "dialed" on the test trunk thereby providing connectivity to the desired MIU device or devices.
Now that the basic structure of a conventional AMR system has been depicted, the operation of a typical AMR system is discussed in more detail. One of the advantages of these systems is that the operational scenarios for AMR procedures are relatively straightforward. If there is any contention for the subscriber line while the AMR procedures are underway, the AMR equipment should disengage itself.
Returning again to FIG. 2, in its quiescent state the MIU 35 is always anticipating the reception of an alerting signal. This alerting signal is originated by the AMR controller at the central office when there is a need to communicate with an MIU located on particular customer's premises. MIU 35 often includes a low power (micro-power) detector circuit for detecting the presence of the alerting signal, such circuit being powered from the phone line by "leakage" current. In this example, the AMR controller at the central office will only generate the alerting signal if the subscriber phone line is "on-hook", i.e. available.
MIU telemetry devices may be either of the outbound or inbound type. For purposes of this application, "outbound" telemetry devices are those telemetry devices which are couplable to a phone line and which are selectively activated by an alerting signal sent over the phone line from a central source. Thus, the particular MIU described above is an example of an outbound telemetry device. In contrast, "inbound" telemetry devices are devices which are couplable to a phone line at a subscriber's site and which dial in to a central location to communicate information to such location. Such inbound telemetry devices typically include a real time clock which causes the device to wake up and dial in to the central location at a predetermined time. MIU's which are of the inbound telemetry devices type may be employed where the environment is appropriate.
Returning to the present example of FIG. 2 which depicts an outbound telemetry device type of MIU, the earlier mentioned alerting signal could be a tone of specified frequency, amplitude and duration while the detector is a selected tone detector which is capable of recognizing the specified frequency, amplitude or duration. Upon reception of the alerting signal, the MIU will "seize" the phone line and typically uses the loop current drawn from the central office switch (20-80 MA) to bias itself to a fully powered-up condition. This fully powered-up state during which the MIU has seized the phone line is referred to as the active mode of the MIU, as opposed to the quiescent mode of the MIU during which the MIU is awaiting the alert signal.
Using a predetermined signalling protocol, a microprocessor within the MIU sends telemetry data (meter reading information) down the phone line to the waiting AMR controller which initiated the alerting signal. The design of the typical MIU is such that the alerting signal can only be acted on if the phone line is "on-hook", this is, the line is not is use. Stated alternatively, when the subscriber line is active, the MIU disengages itself from the phone system. Thus, in the unlikely event that an alerting signal might be present during an ongoing phone conversation (voice falsing) or data exchange (computer modem) the MIU cannot be inadvertently activated.
In more detail, separate so called "static off-hook" detectors and "dynamic off-hook" detectors were provided in prior MIU's to avoid the above described contention situations where the phone user and MIU would potentially conflict in their use of the common phone line. Prior to the present invention, the terms "static off-hook" and "dynamic off-hook" detector were often used. (Quite often the terms could be related directly to separate clusters of individual circuit elements which each performed the respective referenced function.) The descriptive terms "static" and "dynamic" described the MIU state at the time the telephone set was lifted "off-hook", presumably by a subscriber who wished to place an phone call.
The "dynamic off-hook" detector functionally disengaged the MIU from the subscriber line if the MIU was currently active, i.e. sending telemetry data to the AMR controller. In contrast, the "static off-hook" detector prevented the MIU from becoming active at times when the telephone set is off-hook. MIU devices of the prior art typically had separate circuit elements which were alternately engaged in the "static" mode and disengaged in the "dynamic" mode.
In conventional MIU's, some time after the telemetry exchange between the MIU and the AMR controller is completed, the MIU releases the phone line, restoring it to an idle condition. The MIU then returns to the quiescent state and awaits the reception of another alerting signal. However, the possibility exists of a microprocessor malfunction or other malfunction which could cause the MIU to never release the phone line back to the on-hook condition.
To prevent this from occurring, conventional MIU's typically include a watchdog timer which is activated when an alerting signal is received by the MIU. Then, after a predetermined period of time set by the watchdog timer, the MIU is forced to restore the phone line back to the on-hook condition. The predetermined time period associated with the watchdog timer is generally a relatively long period of time, for example 4-5 minutes or longer, so as to be sufficiently long to accommodate the longest anticipated telemetry transmission. However, many telemetry data transmissions last only a few seconds. In these instances, much time may be wasted if the MIU has to rely on a watchdog timer to instruct the MIU to disengage from the telephone line and return use of the line to the phone subscriber.